More Daylight, Less Depression and Better Sleep
Large-scale data links outdoor light exposure to lower depression risk and fewer sleep issues
Our internal clock, aka circadian rhythm, regulate bodily functions from sleep to mood, and they rely on strong light-dark cycles to stay on track.
But modern life of dim offices, glowing screens, and late-night scrolling disrupts these rhythms. This contributes to poor sleep and low mood, even clinical depression, a population-based study shows.
The Study
The authors analyzed data from the UK Biobank, a cohort of over 400,000 adults aged 37–73. A subset of 20,000 participants was tracked over time, and about 160,000 completed detailed mental health questionnaires.
Participants reported their average hours spent outside in summer and winter, which was used to estimate daily daylight exposure.
Key Findings
Most people got only 2.5 hours of outdoor light per day.
More daylight = a healthier body clock. People who spent more time outside were more alert in the morning, and had fewer sleep issues.
More daylight = better mood. They were less likely to experience depression, use antidepressants, or report anxiety, and low interest in activities.
These benefits held even after accounting for age, sex, exercise, sleep, job status, season of assessment, and social life (measured with the question “how often do you visit friends or family or have them visit you”, per week).
Daylight and Mental Health: A Two-Way Street
Daylight predicts future mood. People exposed to more daylight early on were less likely to report depression or anxiety years later.
Mood affects daylight habits. Those feeling down or anxious were less likely to seek sunlight later, suggesting a possible feedback loop: low mood leads to less light exposure, which worsens mood.
Study Limitations
The UK Biobank sample primarily consists of healthy, middle-aged to older adults, which limits the ability to generalize the findings to younger populations, older adults, or those with significant health conditions.
Given that circadian rhythms, sleep patterns, and mood can change significantly across the lifespan, the results observed in this age group might not apply to younger individuals or older adults. For example, circadian rhythms tend to shift with age, and sleep quality can decrease in older age, potentially altering how outdoor light exposure impacts these outcomes.
Takeaways
→Get outside early in the day, as much as possible.
→Prioritize daily outdoor time, even if it’s cloudy. If you can’t get outside in the morning, try to make time to do so at some point.
→Think of sunlight-daylight as part of your Health regimen. You eat to nourish. You workout to feel strong, which makes you feel better. Consider daylight exposure as part of your overall Health.